The possibility of obtaining an increased amount of stem cells and haematopoietic progenitors in circulation in the peripheral blood of a mammal, and in particular in that of a human being, has for years been the subject of intensive research activity, the availability of stem cells and/or haematopoietic progenitors is in fact particularly important in sectors such as the autologous transplantation of circulating haematopoietic progenitors, the allotransplantation of circulating haematopoietic progenitors and in program for the gene therapy of circulating haematopoietic cells.
Although, after birth, stem cells and progenitor cells are located almost exclusively in the bone marrow, they nevertheless exhibit migratory properties; that is to say, under physiological conditions, they migrate through the cavities of the bone marrow and pass into circulation. That process, commonly known as “mobilisation”, can be amplified in mammals by various treatments, such as, for example, the administration of cytokines and, in particular, the growth factor of granulocyte colonies (G-CSF); the reverse process, known as “homing”, occurs, for example, in irradiated receivers after the transplantation of haematopoietic cells; the mechanisms on which mobilisation and homing are based are, however, still obscure (C. F. Craddock et al., “Antibodies to VLA4 Integrin Mobilize Long-Term Repopulating Cells and Augment Cytokine-Induced Mobilization in Primates and Mice”, Blood, Vol. 90, n. 12, 1997, pp. 4779-4788; F. Prosper et al., “Mobilization and Homing of Peripheral Blood Progenitors is Related to Reversible Downregulation of o.4151 Integrin Expression and Function”, J. Clin. Invest., Vol. 101, n. 11, 1998, pp. 2456-2467; M. Vermeulen et al., “Role of Adhesion Molecules in the Homing and Mobilization of Murine Hematopoietic Stem and Progenitor Cells”, Blood, Vol. 92, n. 3, 1998, pp. 894-900).